This invention relates to color picture tubes and particularly to such tubes having a slit type apertured mask.
Shadow mask type color picture tubes usually include a screen of red, green and blue emitting phosphor lines or dots, electron gun means for exciting the screen and a shadow mask interposed between the gun means and the screen. The shadow mask is a thin multiapertured sheet of metal precisely disposed adjacent the screen so that the mask or apertures are systematically related to the phosphor lines or dots.
Color picture tubes having shadow masks with slit shaped apertures have received relatively recent commercial acceptance. One of the reasons for this acceptance is that the percentage of electron beam transmission through the mask can be made higher for a slit mask-line screen type of tube than for a circular apertured mask-dot screen type tube. Even though the use of a slit mask provides a definite advantage in electron beam transmission, the percentage of electron beam transmission through a slit mask can be increased even further than is practiced in the present art.
Two types of slit shadow masks are in present use. In one type, the slits extend continuously from the top to the bottom of the mask. Such configuration is only used in a cylindrically shaped mask and requires a massive rigid frame to hold the mask taut. In another type slit shadow mask, the mask is domed so that it is curved both vertically and horizontally. In this mask embodiment, the vertically extending slits are interrupted by a plurality of spaced bridges or webs to aid in maintaining the domed shape. The presence of these webs, however, reduces electron beam transmission and thereby reduces the amount of tube brightness compared to a tube having no webs. It is therefore desirable to develop a mask wherein the effect of the webs on electron beam transmission is reduced.